A process for preparing a silicon epitaxial wafer. The wafer has a front surface having an epitaxial layer deposited thereon, a back surface, and a bulk region between the front and back surfaces, wherein the bulk region contains a concentration of oxygen precipitates. In the process, the wafer is first subjected to an ideal oxygen precipitating heat treatment to causes the formation of a non-uniform distribution of crystal lattice vacancies with the concentration of vacancies in the bulk region being greater than the distribution of vacancies in the front surface. The ideal precipitating wafer is then subjected to an oxygen precipitation heat treatment to cause the nucleation and growth of oxygen precipitates to a size sufficient to stabilize the oxygen precipitates, with the oxygen precipitates being formed primarily according to the vacancy profile. An epitaxial layer is then deposited on the surface of the oxygen precipitate stabilized wafer.
Legal claims defining the scope of protection, as filed with the USPTO.
1. A process for the preparation of a silicon wafer comprising a front surface having an epitaxial layer deposited thereon, a back surface, a central plane between the front and back surfaces, a front surface layer which comprises the region of the wafer between the front surface and a distance, D 1 , measured from the front surface and toward the central plane, and a bulk layer which comprises the region of the wafer between the central plane and front surface layer, the bulk region further comprising a concentration of oxygen precipitates, wherein the process comprises: subjecting the wafer to a heat-treatment to form crystal lattice vacancies in the surface layer and the bulk layer; and controlling the cooling rate of the heat-treated wafer to produce a wafer having a non-uniform concentration of vacancies with the concentration of vacancies in the bulk layer being greater than the concentration of vacancies in the surface layer such that, upon subjecting the wafer to an oxygen precipitation heat treatment, a denuded zone is formed in the surface layer and oxygen clusters or precipitates are formed in the bulk layer with the concentration of the oxygen clusters or precipitates in the bulk layer being primarily dependant upon the concentration of vacancies; and subjecting the silicon wafer to an oxygen precipitation heat treatment to cause the nucleation and growth of oxygen precipitates in the bulk layer, to a size sufficient to stabilize the oxygen precipitates such that they are incapable of being dissolved at temperatures not in excess of 1150 C.; and, depositing an epitaxial layer on at least one surface of the oxygen precipitate stabilized wafer.
2. The process of claim 1 wherein D 1 is at least about 20 micrometers.
3. The process of claim 1 wherein D 1 is at least about 50 micrometers.
4. The process of claim 1 wherein D 1 is between about 30 and about 100 micrometers.
5. The process of claim 1 wherein said heat-treatment to form crystal lattice vacancies comprises heating the wafers to a temperature in excess of about 1175 C. in a non-oxidizing atmosphere.
6. The process of claim 1 wherein said heat-treatment to form crystal lattice vacancies comprises heating the wafers to a temperature in excess of about 1200 C. in a non-oxidizing atmosphere.
7. The process of claim 1 wherein said heat-treatment to form crystal lattice vacancies comprises heating the wafers to a temperature in the range of about 1200 C. to about 1275 C. in a non-oxidizing atmosphere.
8. The process of any one of claims 1 - 7 wherein said non-oxidizing atmosphere is a nitriding atmosphere.
9. The process of claim 8 wherein said nitriding atmosphere is selected from a group consisting of nitrogen and ammonia.
10. The process of claim 9 wherein said nitriding atmosphere is nitrogen.
11. The process of claim 10 wherein said nitriding atmosphere further comprises oxygen.
12. The process of claim 1 wherein said cooling rate is at least about 20 C. per second through the temperature range at which crystal lattice vacancies are relatively mobile in silicon.
13. The process of claim 1 wherein said cooling rate is at least about 50 C. per second through the temperature range at which crystal lattice vacancies are relatively mobile in silicon.
14. The process of claim 1 wherein said cooling rate is at least about 100 C. per second through the temperature range at which crystal lattice vacancies are relatively mobile in silicon.
15. The process of claim 1 wherein said cooling rate is about 100 C. per sec to about 200 C. per second through the temperature range at which crystal lattice vacancies are relatively mobile in silicon.
16. The process of claim 1 wherein the oxygen precipitation heat treatment comprises heating the wafer to a temperature of at least about 800 C. for a period of time sufficient to cause the nucleation and growth of oxygen precipitates in the bulk layer, to a size sufficient to stabilize the oxygen precipitates such that they are incapable of being dissolved at temperatures not in excess of 1150 C.
17. The process of claim 16 wherein the wafer is heated for a period of time of at least about 4 hours.
18. The process of any one of claims 16 or 17 further comprising heating the wafer to a temperature of at least about 1000 C. for at least about 16 hours.
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August 13, 2001
March 25, 2003
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